The invention relates to the art of phase detection. It is applied in particular to a phase locked loop (PLL) in which context it affords cancellation of periodic "noise" and harmonics effects, while avoiding modulation of the frequency of the VCO of the PLL by the output ripple of the phase detector. The invention is readily implemented with solid state devices.
Reference is made to "Phase Lock Techniques" by Floyd M. Gardner, published by John Wiley-1967, second printing, pgs. 1-16, chapters 1 and 2.
It is known from U.S. Pat. No. 3,944,938 of Michel Brouant to compare two signals of different phases by modulation of one by the other at the input of an integrator for phase control. However, this does not teach phase detection in a sample and hold manner as disclosed herein, nor for phase detection per se.